The present invention relates to catalysts having a bimodal pore radius distribution and comprising a) zirconium dioxide and, if desired, b) aluminum oxide, titanium dioxide and/or silicon oxide and c) at least one element of main group I or II, an element of transition group III, an element of transition group VIII, of the Periodic Table of the Elements, lanthanum and/or tin.
U.S. Pat. No. 5,220,091 discloses catalysts comprising Pt/Sn as active component on a Zn spinel support for the dehydrogenation of small hydrocarbon molecules such as isobutane using steam as diluent. The performance of these catalysts is in need of improvement since, despite the high dilution of the feed with steam (ratio 4:1), only relatively low yields and selectivities are achieved at high reaction temperatures of 600xc2x0 C. Likewise deserving of improvement is the operating life of the catalysts, since they have to be regenerated after an operating time of only 7 hours.
U.S. Pat. No. 4,788,371 discloses Pt/Sn/Cs/Al2O3 catalysts for the dehydrogenation of hydrocarbons using steam dilution (e.g. steam/propane=10:1). Despite the high degree of dilution, only low conversions of 21% are achieved.
WO-A-94/29021 discloses catalysts based on mixed oxides of magnesium and aluminum and further comprising a noble metal of group VIII, a metal of group IVa and, if desired, an alkali metal of group Ia, of the Periodic Table of the Elements for the dehydrogenation of, for example, a gas mixture of H2O/propan/H2/N2 in a ratio of 8:7:1:5. A drawback of these catalysts in industrial applications is their low hardness, which makes industrial use difficult. Furthermore, the performance of these catalysts, in particular at low reaction temperatures, is in need of improvement. A further disadvantage is the complicated operating procedure which, to maintain the performance, requires the addition of hydrogen to the feed and the mixing in of nitrogen for further dilution.
It is an object of the present invention to remedy the abovementioned disadvantages.
We have found that this object is achieved by new and improved catalysts having a bimodal pore radius distribution and comprising
a) from 10 to 99.9% by weight of zirconium dioxide and
b) from 0 to 60% by weight of aluminum oxide, silicon dioxide and/or titanium dioxide and
c) from 0.1 to 10% by weight of at least one element of main group I or II, an element of transition group III, an element of transition group VIII, of the Periodic Table of the Elements, lanthanum and/or tin,
with the proviso that the sum of the percentages by weight is 100, a process for the dehydrogenation of C2-C16-hydrocarbons and the use of these catalysts for this purpose and also a process for producing these catalysts.